Updating a behavior object array in Angular 5 by appending data to the end

Question

Updating a behavior object array in Angular 5 by appending data to the end

After creating a service to share data across my entire application, I'm wondering if it's possible to append new data to an array within the userDataSource. Here is how the service looks:

user.service

userDataSource = BehaviorSubject<Array<any>>([]);

userData = this.userDataSource.asObservable();

updateUserData(data) {
    this.userDataSource.next(data);
}

In my component, I make an API call and then send that data to userDataSource like this:

constructor(
private: userService: UserService,
private: api: Api
){
}

ngOnInit() {
    this.api.getData()
      .subscribe((data) => { 
         this.userService.updateUserData(data);
      })
}

Everything works fine so far, but now I want to know if I can add data to the end of the array inside userDataSource without overwriting existing data. Essentially, I want to achieve something similar to using .push. Would simply calling the updateUserData() function with additional data work in this case?

Any assistance on this matter would be greatly appreciated.

javascript angular typescript

Answer 1

Answer №1

If you want to enhance your service, consider creating a new method such as addData. This method allows you to merge existing data with new data effortlessly.

import {Injectable} from '@angular/core';
import {BehaviorSubject} from 'rxjs/BehaviorSubject';

@Injectable() 
export class UserService {
    userDataSource: BehaviorSubject<Array<any>> = new BehaviorSubject([]);

    userData = this.userDataSource.asObservable();

    updateUserData(data) {
        this.userDataSource.next(data);
    }

    addData(dataObj) {
        const currentValue = this.userDataSource.value;
        const updatedValue = [...currentValue, dataObj];
        this.userDataSource.next(updatedValue);
    }
}

Answer 2

If you want to enhance your service, consider creating a new method such as addData. This method allows you to merge existing data with new data effortlessly.

import {Injectable} from '@angular/core';
import {BehaviorSubject} from 'rxjs/BehaviorSubject';

@Injectable() 
export class UserService {
    userDataSource: BehaviorSubject<Array<any>> = new BehaviorSubject([]);

    userData = this.userDataSource.asObservable();

    updateUserData(data) {
        this.userDataSource.next(data);
    }

    addData(dataObj) {
        const currentValue = this.userDataSource.value;
        const updatedValue = [...currentValue, dataObj];
        this.userDataSource.next(updatedValue);
    }
}

Answer 3

Answer №2

If you ever encounter a situation involving a

BehaviorSubject<YourObject[]>

, I stumbled upon a solution in a blog post titled this article.

import { Observable, BehaviorSubject } from 'rxjs';
import { YourObject} from './location';
import { Injectable } from '@angular/core';
@Injectable({
    providedIn: 'root'
})
export class ObjService {
    private theObjData: BehaviorSubject<YourObject[]> = new BehaviorSubject<YourObject[]>(null);

    constructor() {
    }

    public SetObjData(newValue: YourObject[]): void {
        this.theObjData.next(Object.assign([], newValue));
    }
}

To update the data:

// inside some component
this.api.userData().subscribe((results:YourObject) => 
    this.objService.SetObjData(results);
)

To observe changes on another component:

// inside another component
ngOnInit() {
    this.objService.GetAccountStatements().subscribe((results) =>
    ...
    )
}

Answer 4

If you ever encounter a situation involving a

BehaviorSubject<YourObject[]>

, I stumbled upon a solution in a blog post titled this article.

import { Observable, BehaviorSubject } from 'rxjs';
import { YourObject} from './location';
import { Injectable } from '@angular/core';
@Injectable({
    providedIn: 'root'
})
export class ObjService {
    private theObjData: BehaviorSubject<YourObject[]> = new BehaviorSubject<YourObject[]>(null);

    constructor() {
    }

    public SetObjData(newValue: YourObject[]): void {
        this.theObjData.next(Object.assign([], newValue));
    }
}

To update the data:

// inside some component
this.api.userData().subscribe((results:YourObject) => 
    this.objService.SetObjData(results);
)

To observe changes on another component:

// inside another component
ngOnInit() {
    this.objService.GetAccountStatements().subscribe((results) =>
    ...
    )
}

Answer 5

Answer №3

Typically, Observables and Subjects are designed to function as continuous streams of data rather than simply storing data. However, BehaviorSubjects differ in that they retain the last value emitted.

In general, it's recommended for Subjects or BehaviorSubjects within a encapsulated class (like a Service) not to be exposed publicly to other classes. Instead, accessing their properties through getters or methods helps maintain the integrity of the data stream by keeping it isolated from subscribers.

Nevertheless, given the nature of BehaviorSubject holding the most recent emitted value, there are various approaches available. If all subscribers require a combined stream of data from each emission, you can access the last emitted value and append to it:

userDataSource = BehaviorSubject<any[]>([]);

userData = this.userDataSource.asObservable();

updateUserData(data) {

    this.userDataSource.next(this.userDataSource.value.push(data));
}

Alternatively, for what could be considered a more advisable practice, subscribers to this Subject can perform their own transformation on the stream:

this.api.userData()
  .scan((prev, current) => prev.push(current). [])
  .subscribe((data) => { 
     this.concatenatedUserData = data;
  });

Answer 6

Typically, Observables and Subjects are designed to function as continuous streams of data rather than simply storing data. However, BehaviorSubjects differ in that they retain the last value emitted.

In general, it's recommended for Subjects or BehaviorSubjects within a encapsulated class (like a Service) not to be exposed publicly to other classes. Instead, accessing their properties through getters or methods helps maintain the integrity of the data stream by keeping it isolated from subscribers.

Nevertheless, given the nature of BehaviorSubject holding the most recent emitted value, there are various approaches available. If all subscribers require a combined stream of data from each emission, you can access the last emitted value and append to it:

userDataSource = BehaviorSubject<any[]>([]);

userData = this.userDataSource.asObservable();

updateUserData(data) {

    this.userDataSource.next(this.userDataSource.value.push(data));
}

Alternatively, for what could be considered a more advisable practice, subscribers to this Subject can perform their own transformation on the stream:

this.api.userData()
  .scan((prev, current) => prev.push(current). [])
  .subscribe((data) => { 
     this.concatenatedUserData = data;
  });

Answer 7

Answer №4

Combine objects using concat method

userDataSource = BehaviorSubject<Array<any>>([]);

updateUserData(data) {
    this.userDataSource.next(this.userDataSource.value.concat(data));
}

Filter out specific object from the array

removeUserData(data) {
    this.userDataSource.next(this.userDataSource.value.filter(obj => obj !== data));
}

Answer 8

Combine objects using concat method

userDataSource = BehaviorSubject<Array<any>>([]);

updateUserData(data) {
    this.userDataSource.next(this.userDataSource.value.concat(data));
}

Filter out specific object from the array

removeUserData(data) {
    this.userDataSource.next(this.userDataSource.value.filter(obj => obj !== data));
}

Updating a behavior object array in Angular 5 by appending data to the end

Answer №1

Answer №2

Answer №3

Answer №4

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